Apparatus for shock gelling nitrocellulose



Feb- 12, 1963 D. E. ELRICK ETA.

APPARA'rus FOR sHocx SELLING NITRocELLuLosE Filed Nov. 21, 1960 INVENTORS. FIG'Z DONALD E. ELRICK WILLIAM H. GARDNER BY aired brutes The present invention relates to an apparatus for leaching the alkoxy alcohol solvent from shock-gelled nitrocellulose casting powder.

in order for the shock-gel process for production of casting powder on a continuous basis to be economically feasible, the diglycol used as a solvent in the operation must be recovered. The extracting apparatuses known and available are both cumbersome and expensive and fail to produce completely leached shock-gelled casting powder. As the potentiality of shock-gelled casting powder grew, the need for eli'icient, continuously operable leaching equipment became apparent.

The problems confronting designers of a suitable apparatus which would function satisfactorily under all the diliicult conditions encountered in etlectively leaching shock-gelled nitrocellulose have been overcome by the present invention.

The primary purpose of this invention is to provide a continuous counter current apparatus for complete extraction of diglycol from the nitrocellulose phase and for the concentration of diglycol in the initial leaching phase. The proper removal of diglycol is necessary in order to produce a uniform product.

The general purpose of this invention is to design an apparatus which in operation utilizes a U-shaped column in which freshly gelled casting powder spheroids move in one direction by pneumatic pulsation while fresh water liows in the other direction. Solvent-free spheroids or balls of water-logged casting powder are removed at one end, and concentrated aqueous diglycol solution is withdrawn at the other end.

An object of the present invention is to provide an automatic counter current extractor with which completely leached shock-gelled casting powder is produced for use in rocket propellant grains.

Another object of the present invention is to provide an apparatus for recovery of diglycol from the nitrocellulose phase which may be re-used.

The exact nature of this invention as well as other objects and advantages will be readily appreciated as the same become better understood by reference to the following detailed description as illustrated in the accompanying sheet of drawing in which:

FIGURE l is a vertical view, partly diagrammatic in character, of an apparatus embodying the present invention; and

FGURE 2 is a larger scale longitudinal section of the pressure valve shown diagrammatically in FIG. 1.

The leaching apparatus shown in FlG. 1 comprises a pump means, diagrammatically illustrated and generally indicated by numeral 16, a dropping pan 17 provided with holes in its bottom, said pan and pump being connected by a flexible conduit i3 made up of 1/2 inch I D. Tygon tubing, the pan being positioned above the pump which is adapted to push liquid into the pan by peristaltic action without actual contact between the liquid and the pump; a U-tube 9 constructed of four inch LD. Pyrex pipe with aluminum fittings and having a left and a right column designated by numerals l@ and 2l respectively, column l@ being about 86 inches in height and column 2l being about 88 inches in height, a leaching container i9 connected to the midportion of left column le of U-tube 9 by a tubular elbow M with a constricted passage l5, and an exit orifice 25 near its top through which concentrated diglycol solution is withdrawn; an inlet il through which air at constant pressure is introduced into column in; a valve l2 mounted on column l@ for controlling the air pressure on the contents of the column and consisting of two pieces of concentric cellulose acetate tubing, the outer piece being stationary and the inner piece being movable relative thereto and driven by a constant speed motor i3, the pieces of tubing having openings therein such that with movement of the inner piece the pressure is iirst increased rapidly and then gradually released, thereby pulsating the contents of column lil for pushing the contents forward rapidly and then allowing them to settle slowly; a owmeter attached to the top of column 21 for introducing and regulating a countercurrent of water into column 2?.; an exit tube 22 about midway on column 2l for the exit of the spheroids; a gate valve 2d at the end of tube 22 and a portable container 23. FIG. 2 shows a longitudinal section of valve 212 mounted on column lit by a metal pipe coupling 36 for controlling the air pressure on the contents of said column. Valve i2 consists of two pieces of concentric cellulose acetate tubing, the outer tubing 2e having an opening 28 approximately 3%; x 3%; inch square in size and the inner tubing Si?, being movable relative thereto and having a triangular slit opening 32, approximately 3A x 2.5 X 2.5 inches in size and being attached to a rubber stopper 34 which supports a steel rod 35 connected to speed motor 13 for rotating inner tubing 36 in the direction of the arrow 37. Air pressure is constantly supplied through an opening l1 below valve 12.

The preferred pump means lo used in the present invention is a peristaltic type known as a Sigmamotor pump, which is designed to handle liquids, slurries or gases. It operates by means of a series of cam operated fingers which pass against flexible tubing 1S in sequence and impart a positive unidirectional movement to fluid (nitrocellulose solution) in the tube. The material being pumped does not come in Contact with the pump parts so no contamination results and no cleaning of the pump is necessary. The pump is designed to use tygon, gum rubber, or neoprene tubes of varying internal diameters. Various pump combinations are available including motors and belt drives and variable speed units. The pumping combination utilized in the present invention is composed of a Sigmarnotor pump, a 1% HP. hydraulic` transmission and a 1/2 HP. electric motor mounted on a base. Other suitable means may be used to introduce the nitrocellulose solution to the dropping pan; however, this preferred means eliminates the hazard that is associated with pumping nitrocellulose solution since the huid being pumped does not come into direct contact with the pump parts.

In operation, nitrocellulose casting powder-diglycol solution is forced by Sigmamotor pump means lo through tubing 18 to a dropping pan t7. Dropping pan 17 is proenvases vided with numerous holes through which the solution passes thereby forming drops. These drops of nitrocellulose-diglycol are shock-gelled in the form of casting powder spheroids in the initial leaching bath 19. The shock-gelled particles fall through constriction to the bottom of the Uetube 9. The pulsating movement imparted to the water and the weight of the additional powder causes the spheroids to be gradually forced up column 21. The level of the spheroids in column 10 of U-tube 9 remain essentially constant except for an oscillating motion. The contents of U-tube 9 are oscillated by fluctuation of the air pressure controlled by the operation of valve 12 in which the inner tubing 30 rotates in a direction such that the point of slit 32 first crosses the first vertical edge of the square opening 28 in the outer tube 26. Continued rotation allows a gradually increasing opening in the inner tubing to be opposite that of the square opening 28 in the outer tubing 26 until the rear edge of the slit 32 coincides with the first vertical edge of the square opening. Then the opening through the tubes decreases until the rear edge of slit 32 passes the second vertical edge of the square opening Z8. At this point pressure builds up rapidly and is abruptly applied on the water in column 10 which causes the water and pellets to be forced upward in column 21. To keep the force diverted in a downward direction in column 10, tubular extension 14 of the leaching bath 19 is constricted at 15 by means of a 1/s inch rubber sheeting containing an opening 1/3/16 inches in diameter. When the inner tubing 30 of valve 12 has rotated so that the slit again allows pressure to be decreased slowly by allowing the air to be bled off through the opening, the water in column 21 recedes slowly and the spheroids or pellets tend to stay at the height to which they were forced. The combination of newly formed pellets in the bottom of column 10 and each additional pulsation tends to force the pellets higher in column 21 until they overflow into the side arm tube 22. As the spheroids are forced up column 21, a countercurrent flow of water is introduced through a owmeter 20. Air-free water was found to be the most satisfactory, since tap water caused bubbles to collect on the spheroids which produced a buoyant effect. The diglycol is continuously removed from the freshly gelled spheroids until complete leaching has occurred with the aqueous phase becomingV gradually enriched with diglycol. The concentrated aqueous diglycol solution is exhausted through exit 25. When equilibrium is established a gradient of concentration ofV diglycol ranging from pure water at point A of exit 22 to 25-45% aqueous diglycol at point B of exit 25 exists inl the aqueous phase. The solution inside the shock-gelled powder ranged from being diglycol-free at the point of exit 22 for said spheroids to being concentrated in diglycoll at the bottom of column 10. When the leached spheroids are forced toward the top of column 21, the spheroids fall into tube 22' from which they are removed by means of a two inch gate valve 24. This valve is opened to permity the spheroids to fall into container 23. The-removal of the leached powder is the only phase of this process which requires manual operation.

Data from three runs are summarized below. The timeA in lminutes was measured from initial dropping of nitrocellulose casting powder-diglycol solution. The concentration of diglycol was determined by refractive index measurements. The accuracy of this method is limited to 0.2 to 0.4% diglycol which is in the range found in the leached balls in Tables Il and III. The weights of the wet powder and consequently the dry powder were approximated.

Conditions for the three runs were essentially the saine except for the rate of addition of water to the column. A rate of 200 ml./min. was not fast enough in the first run as the refractive index measurements indicated a fairly large amount of diglycol remained in the shock-gelled nitrocellulose. A rate of400 ml./min. was too--fast in the second run as the efiiuent was of a low concentration.

The rate of 270 nil/min. in the final run gave spheroids that were essentially diglycol free and a 29% concentration of diglycol in the effluent.

Table I t. Percent Percent Time Wet D G in D G in (min.) Powder Wet Effluent (g.) Powder 1,700 0.1 30.5 Water rate, 20.0 11:11./ 1,700 36.0 min. to 198 min. and 1,700 39.5 220 mLImin. to 318 1,700 40.7 min. 1,700 42.0 1,700 42.6 1,700 41 7 1,700 41.8 1, 700 41.3 1,700 41.0 1,700 40.2 1,700 38.3 1,700 0.5 37.0 20, 400 0.82lb/ r. (dry Weight) Table Il Wt. Percent Percent Time Wet DG in DG in (min) Powder Effluent Wet (g.) Powder Vater, 410 ml.lmin. to 150 rnin. and 300 IDL/min. to 280 min.

0.3 27.2 0.78 1b./nr. (dry weight) Table III Wt. Percent Percent Time. Wet D G in DG in (min.) Powder Wet Effluent (g.) Powder Water rate 270 1311./

0.1 25.1 min. Casting Pow- 0.4 27.1 der DG rate g.l 0.2 28.7 min. 0.4 28.3 0.3 28.6 0.2 29.0 0.4 28.6 0.3 28.7 0.73 b./hr. (dry eight) Variousimodifications arecontemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter defined by the appended claims.

What is claimed is:

1. Apparatus for leaching granular nitrocellulose, said apparatus comprising a pump having extending therefrom` a conduit, a dropping pan provided with holes in its` bottom, said pan and pump being connected by said conduit and the pan positioned on a level above the pump, an initial leaching bath container provided with, an exit orifice near its top and' a tubular extension in communication with one column of a U-tube at a point lower than the container and about midway of said column of the U-tube, said dropping pan positioned ad, jacent said leaching bath container,` a valve positioned at the top of said one column of the U-tube adapted to control the airepressure in said column, a flowrneterpositioned attire-top of the othercolurnn of-said Lt-tube for providing constant countercurrent flow of Water, anl

exit tube positioned about midway on the said other column of said U-tube and a gate valve means at the end of said exit tube.

2. In an apparatus for shock-gelling and leaching granular nitrocellulose, the combination comprising a pump, a dropping pan provided with holes in its bottom; said pan and pump being connected by a iiexible tubing, said pan being located above said pump, and said pump being adapted to pump liquid into said pan by peristaltic action without actual contact between the liquid and the pump; a U-tube having a right and a left column; a leaching bath container connected to said left column by a conduit having a constricted passage, said container having an exit orifice near its top; said U-tube being arranged with the leaching bath container directly underneath said dropping pan, whereby the solution to be leached flows through the holes in said pan thereby forming drops which fall into said leaching bath container to be shock-gelled into spheroids, said spheroids falling through said conduit and into said left column, said constricted passage acting as a check means to prevent reverse movement of said spheroids up the conduit; means attached to the top of said right column for introducing and regulating a countercurrent of water into said right column, said right column being provided with an exit tube below its top for the exit of the spheroids, and means connected to said left column for imparting a pulsating movement to the contents of the U-tube, said valve means comprising inner and outer tubings concentrically arranged, the outer tubing being attached to the top of the left column and having a square opening, the inner tubing having a triangular opening and moving relative to the outer tubing; whereby said spheroids are forced through the U-tube and into the exit tube and excess Water is forced out of the exit orifice of the leaching bath container.

3. An apparatus for shock-gelling nitrocellulose comprising, a U-tube having a left and a right column, a leaching container connected to the midportion of said left column by a tubular elbow having a constricted passage and an exit orifices near its top; an air inlet positioned near the top of said left column through which air -at constant pressure is introduced; a valve means mounted at the top of said left column through which air at constant pressure is introduced, said valve means comprising inner and outer tubings concentrically arranged, the outer tubing being attached to the top of the left column and having a square opening, the inner tubing having a triangular opening and rotatable relative to the outer tubing and driven by a constant speed means for the purpose of pulsating the contents of said left column; a flowmeter attached to the top of said right column for introducing and regulating a counter-current of water into said right column; an air exit elbow about midway on said right column having a gate valve at its end for exit of nitrocellulose; a dropping pan provided with holes in its bottom positioned above said leaching container and having a conduit extending therefrom connected to a means adapted for pushing nitrocellulose solution through said conduit into said pan.

References Cited in the file of this patent UNITED STATES PATENTS 2,189,387 Wissler Feb. 6, 1940 2,223,747 Suss Dec. 3, 194() 2,332,157 Mapson Oct. 19, 1943 2,381,965 Berry Aug. 14, 1945 2,448,439 Kimberlin et al Aug. 31, 1948 2,744,066 Spiess et al. May 1, 1956 2,923,033 Baldwin Feb. 2, 1960 FOREIGN PATENTS 341.581 Great Britain Ian. 22, 1931 

1. APPARATUS FOR LEACHING GRANULAR NITROCELLULOSE, SAID APPARATUS COMPRISING A PUMP HAVING EXTENDING THEREFROM A CONDUIT, A DROPPING PAN PROVIDED WITH HOLES IN ITS BOTTOM, SAID PAN AND PUMP BEING CONNECTED BY SAID CONDUIT AND THE PAN POSITIONED ON A LEVEL ABOVE THE PUMP, AN INITIAL LEACHING BATH CONTAINER PROVIDED WITH AN EXIT ORIFICE NEAR ITS TOP AND A TUBULAR EXTENSION IN COMMUNICATION WITH ONE COLUMN OF A U-TUBE AT A POINT LOWER THAN THE CONTAINER AND ABOUT MIDWAY OF SAID COLUMN OF THE U-TUBE, SAID DROPPING PAN POSITIONED ADJACENT SAID LEACHING BATH CONTAINER, A VALVE POSITIONED AT THE TOP OF SAID ONE COLUMN OF THE U-TUBE ADAPTED TO CONTROL THE AIR PRESSURE IN SAID COLUMN, A FLOWMETER POSITIONED AT THE TOP OF THE OTHER COLUMN OF SAID U-TUBE 